Jiang-Kai Qiu

Catalytic Dual 1,1-H-Abstraction/Insertion for Domino Spirocyclizations.

A catalytic domino spirocyclization of 1,7-enynes with simple cycloalkanes and cyclo-1,3-dicarbonyls has been established via multiple C-C bond formations from alkynyl/alkenyl functions and dual α,α-C(sp(3))-H abstraction/insertion. The reaction involves addition, 6-exo-dig cyclization and radical coupling sequences under convenient catalytic conditions and provides a concise access to spiro cyclopenta[c]quinolines in good to excellent yields.

Catalytic Arylsulfonyl Radical Triggered 1,7-Enyne Bicyclizations

A new metal-free bicyclization reaction of 1,7-enynes anchored by α,β-conjugates with arylsulfonyl radicals generated in situ from sulfonyl hydrazides has been established using tert-butyl hydroperoxide and tetrabutylammonium iodide. The reactions occurred through sulfonylation/6-exo-dig/6-exo-trig bicyclization/in situ desulfonylation/5-exo-trig cyclization/alkyl or alkenyl migration cascade mechanism to give benzo[j]phenanthridines regioselectively.

Metal-Free Iodine-Catalyzed Synthesis of Fully Substituted Pyrazoles and Its Sulphenylation

A direct and metal-free access toward fully substituted pyrazoles and its sulphenylation has been established through an iodine-mediated three-component [3 + 2] annulation of β-ketonitrile (or pentane-2,4-dione), arylhydrazines, and aryl sulfonyl hydrazides. The reaction allows the formation of one C-S and two C-N bonds by the multiple bond cleavage including sulfur-oxygen, sulfur-nitrogen, and carbon-oxygen bonds. The method features low-cost and readily accessible substrates, bond-forming efficiency, and broad substrate scopes as well as simple one-pot operation, which makes this strategy highly attractive.

Silver-Mediated Radical C(sp3)–H Biphosphinylation and Nitration of β-Alkynyl Ketones for Accessing Functional Isochromenes

Silver-mediated C(sp3)-H functionalization and 6-endo-dig oxo-cyclization of conjugated β-alkynyl ketones have been established under oxidative conditions. The reaction leads to the concise formation of a wide range of isochromenes via C(sp3)-H bond-breaking and radical addition steps. Dual and monofunctional isochromene products were selectively controlled by using either electron-rich or electron-deficient radical sources.

I2-Catalyzed Multicomponent Reactions for Accessing Densely Functionalized Pyrazolo[1,5-a]pyrimidines and Their Disulphenylated Derivatives

New I2-catalyzed multicomponent bicyclization reactions of β-ketonitriles with sulfonyl hydrazides have been established, providing a direct and metal-free access toward unreported pyrazolo[1,5-a]pyrimidin-4-ium sulfonates. The latter could be quantitatively converted into densely functionalized pyrazolo[1,5-a]pyrimidines in the presence of bases. Using sulfonyl hydrazides as a sulfenylating agent, the resulting pyrazolo[1,5-a]pyrimidines enabled I2-catalyzed unprecedented disulphenylations to access fully substituted pyrazolo[1,5-a]pyrimidines through direct C(sp(2))-H bond bifunctionalization.

Metal-free oxidative hydrophosphinylation of 1,7-enynes

A new metal-free oxidative hydrophosphinylation of 1,7-enynes for forming polyfunctionalized 3,4-dihydroquinolin-2(1H)-ones has been realized using readily accessible diarylphosphine oxide and TBPB as an oxidant. The reaction pathway involves an in situ-generated P-centered radical-triggered α,β-conjugate addition/6-exo-dig cyclization/H-abstraction sequence, providing a direct and promising protocol for the formation of C–P, C–C and C–H bonds and rapid construction of complex heterocyclic compounds.

A new [4 + 1]/[4 + 2]bicycliaztion strategy for accessing functionalized indeno[1,2-b]pyran-2-ones

A new base-promoted bicyclization strategy for the synthesis of functionalized indeno[1,2-b]pyran-2-ones has been established from readily accessible o-phthalaldehydes (OPA) and the preformed 1-arylethylidenemalononitriles. The reaction pathway involves an aldol addition, 5-exo-trig carbocyclization and 6-exo-dig oxo-cyclization sequence, resulting in continuous multiple C–C and C–O bond formation.

Cs2CO3-promoted [3 + 2] cycloaddition providing an easy protocol toward imidazo[1,2-a]indole derivatives

A base-promoted [3 + 2] cycloaddition for the construction of multi-functionalized imidazo[1,2-a]indole derivatives with good yields has been accomplished. This transformation provides an easy and facile protocol for the formation of diverse imidazo[1,2-a]indoles of chemical and biomedical importance using preformed 3-sulfonyl-2-sulfonyldiazenyl-1H-indoles and readily available but-2-ynedioates under mild conditions.